Etching a layer or film by reactive ion (sputter) etching is useful in a variety of contexts, more specifically in the art of semiconductor integrated circuit manufacturing. The term "sputter" is added to denote those physical processes, in addition to the chemically reactive processes, which can aid the etching.
For example, a paper authored by J. M. Moran and D. Maydan, entitled, "High Resolution, Steep Profile, Resist Patterns," published in The Bell System Technical Journal, Vol. 58, pp. 1027-1036 (1979), describes a "tri-level" process for generating a desired pattern (of mask portions and window portions) in a relatively thick (2.6 micron) organic film or layer, i.e., a layer of chemically organic material. The bottom surface of the organic layer is conformal with the steps on a top major surface of a VLSI wafer to be selectively etched using, as a selective etch mask, the organic layer after it has been patterned. By "VLSI wafer" is meant a semiconductor body which contains "very large scale integrated circuits" at a major surface thereof. The purpose of the patterning of the organic layer is to enable the use of the resulting patterned organic layer as a mask for selective etching of underlying substance or material of the VLSI wafer at the bottom of the windows.
The top surface of the organic layer before patterning is planar for the purpose of good resolution in the ultimate etch patterning of the VLSI wafer. The chemical composition of the organic layer is typically that of a photoresist material. Patterning of this organic layer is achieved by coating it with a relatively thin (about 0.12 micron) intermediate layer of silicon dioxide and a relatively thin top layer of resist sensitive to x-ray, electron, ion, or optical radiation.
The organic layer together with the intermediate layer of silicon dioxide and the top layer of resist form a "tri-level" system. After exposing the top resist layer to a pattern of x-rays, electrons, or light and subsequently developing this top resist layer in accordance with the pattern (about 0.4 micron thick at mask portions, zero at window portions), the intermediate layer of silicon dioxide is selectively etched in accordance with the pattern by CHF.sub.3 or reactive ion etching, using the thus patterned top resist layer as a selective mask against etching. Next, the thick organic layer is selectively etched to form a patterned organic layer (i.e., patterned with apertures or windows therein) by means of reactive oxygen ion anisotropic (vertical wall) sputter etching in pure oxygen gas, using the thus patterned intermediate silicon dioxide layer as a selective mask (the top resist layer ordinarily being completely removed by the reactive oxygen ion etching). Thereby, the VLSI wafer could be further processed--as by etching, implantation, deposition, etc.--as desired for the fabrication of the integrated circuits at the major surface of the wafer, utilizing the thus patterned organic layer as a selective mask therefore.
Ordinarily, at some time prior to the completion of the integrated circuits, the patterned organic layer is removed, for example, by dissolving the layer by means of a suitable organic solvent, such as a mixture of dimethyl sulfoxide and anhydrous hydrazine, as disclosed in greater detail in the patent application entitled "Removing Hardened Organic Materials During Fabrication of Integrated Circuits," Ser. No. 214,171 filed on Dec. 8, 1980, by E. Kinsbron and F. Vratny, having one of the inventors in common herein.
In a typical case, the material or substance of the VLSI wafer located at the bottom of the windows in the patterned organic layer is essentially metallic aluminum for interconnecting the various integrated circuit elements on the VLSI wafer. In such cases, this aluminum is then selectively anisotropically etched, using the patterned organic layer as an etch mask, by reactive ion etching with a mixture of ions of boron trichloride (BCl.sub.3) and chlorine (Cl.sub.2) with or without added helium. Such reactive ion etching also removes the intermediate silicon dioxide layer of the "tri-level" system. In any event, this etching selectively removes the aluminum only at the bottom of the windows in the patterned organic layer. It has been observed by workers in the art that, after this selective etching of the aluminum, build-ups of material remain on the sidewalls of the windows in the patterned organic layer. These build-ups are not soluble in the organic solvent used to dissolve the patterned organic layer, and therefore these build-ups collapse in pieces onto the surface of the VLSI wafer when the patterned organic layer is dissolved; thereby, the collapsed pieces of these build-ups cause mechanical abrasions or scratches as well as obstruct subsequent VLSI processing steps, such as encapsulation of the VLSI circuits in silicon nitride.
Workers in the art have believed that these sidewall build-ups are formed during the reactive ion etching of the aluminum, as an end-product of that etching. Accordingly, it has not been appreciated that these build-ups can undesirably interfere with the resolution achievable from etching the aluminum using the patterned organic layer as a mask, as well as interfere with the subsequent removal of the patterned organic layer during the ordinary further processing of the VLSI wafer.